1. Field of the Invention
The present invention relates to a spindle motor, for example, loaded with an optical disk such as a mini disk (MD) or the like and operating to drive it.
2. Related Background Art
FIG. 4 is a longitudinal sectional view showing an example of a conventional spindle motor loaded with a disk of relatively large diameter (Φ120) such as a CD, a DVD, or the like, and this spindle motor 20 is composed of a stator section 21 as a fixed section, and a rotor section 22 supported as rotatable relative to the stator section 21 and loaded with the optical disk.
Among these, the stator section 21 is composed of a stator board 23 as a fixture member of this spindle motor 20, a cylindrical housing 24 a lower end of which is fixed in an insert hole in the central region of the stator board 23, a laminated iron core 25 fitted on the outer periphery of the housing 24, a plurality of coils 26 wound on the laminated iron core 25, a sliding bearing 27 pressed into the housing 24, a thrust receiver 24a inserted and fixed in the lower end of the housing 24, and so on.
On the other hand, the rotor section 22 is generally composed of a rotational shaft 28 which is inserted in the sliding bearing 27 and the lower end of which is supported by the thrust receiver 24a, a turn table 29 of approximate disk shape having a longitudinal section of approximately anastatic () shape in which the upper half of the rotational shaft 28 is pressed in the center of a cylindrical portion 29a, a rotor yoke 30 of an approximately anastatic section engaged with a projection formed in the lower center of the turn table 29, the projection being caulked at its outer periphery, an aligning member 32 and an attraction magnet 35 set on the cylindrical portion 29a of the turn table 29, and so on.
Among these components, the rotor yoke 30 is provided with a cylindrical rotor magnet (permanent magnet) 31 the periphery of which is fixed to the inner periphery of the cylindrical portion of the rotor yoke 30 with an adhesive, and this rotor magnet 31 is opposed with a predetermined gap to the outer periphery of the aforementioned laminated iron core 25.
A compression coil spring 33 of a material of a rectangular section is set in a groove formed in a lower surface of the aligning member 32, and the lower end of this compression coil spring 33 is supported by a bottom surface of a groove formed around the lower end of the cylindrical portion 29a of the turn table 29, whereby this compression coil spring 33 is maintained in a compressed state in FIG. 4.
Further, a stopper 34 of annular shape on a plan view is pressed and secured onto a stepped portion formed in an outer peripheral portion at the upper end of the cylindrical portion 29a of the turn table 29, and the annular attraction magnet 35 is set in an annular groove formed at the upper end of the cylindrical portion 29a and is secured with an adhesive.
When the optical disk 36, indicated by chain lines, is mounted on the upper surface of the cylindrical portion 29a of the turn table 29, an inner lower edge of a center hole 36a of the disk is guided in contact with a slant face 32a formed on the outer periphery of the aligning member 32, whereby the optical disk 36 is aligned with the turn table 29 and the rotational shaft 28 through the aligning member 32.
The attraction magnet 35 attracts an attracted plate 38 supported at its outer periphery by a holder 37 mounted on the upper surface of the optical disk 36, whereby the optical disk 36 is maintained in a mounted state while being urged against the turn table 29.
In the spindle motor of this structure, the rotor section 22 is rotated by interaction of magnetic fields generated by energization of the coils 26 and magnetic fields established by the rotor magnet 31 and the rotor yoke 30.
In conjunction therewith, the optical disk 36 is rotated together with the turn table 29 in synchronism with the rotor section 22, while being maintained in the urged state against the turn table 29 by the stopper 37.
In recent optical disk apparatuses equipped with this spindle motor, however, there are demands for further decrease in size and thickness, as is the case with a portable MD or the like, and demands for higher accuracy of positioning of the optical disk in correspondence with increase in density of the optical disk.